Potassium Capture by Kaolin, Part 2: K2CO3, KCl, and K2SO4

Wang, Guoliang; Jensen, Peter Arendt; Wu, Hao; Frandsen, Flemming; Sander, Bo; Glarborg, Peter

doi:10.1021/acs.energyfuels.7b04055

Cited by 41 publications

(42 citation statements)

References 57 publications

(158 reference statements)

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“…The median diameter (D ) of ASV2CFA0-32, ASV2CFA32-45 and ASV2CFAGR was 10.20 μm, 33.70 μm and 6.03 μm, respectively. The D 50 of ASV2CFAGR is comparable with that of kaolin (5.47 μm) and mullite (5.90 μm) utilized in our previous studies [32,33]. A sieving analysis showed that ASV2CFA0-32 contributed 63.0 wt.…”

Section: Methodssupporting

confidence: 75%

KOH capture by coal fly ash

Wang

Jensen

et al. 2019

Fuel

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The KOH-capture reaction by coal fly ash at suspension-fired conditions was studied through entrained flow reactor (EFR) experiments and chemical equilibrium calculations. The influence of KOH-concentration (50-1000 ppmv), reaction temperature (800-1450 °C), and coal fly ash particle size (D 50 = 6.03-33.70 μm) on the reaction was investigated. The results revealed that, at 50 ppmv KOH (molar ratio of K/(Al+Si) = 0.048 of feed), the measured K-capture level (C K ) of coal fly ash was comparable to the equilibrium prediction, while at 250 ppmv KOH and above, the measured data were lower than chemical equilibrium. Similar to the KOH-kaolin reaction reported in our previous study, leucite (KAlSi 2 O 6 ) and kaliophilite (KAlSiO 4 ) were formed from the KOH-coal fly ash reaction. However, coal fly ash captured KOH less effectively compared to kaolin at 250 ppmv KOH and above. Studies at different temperatures showed that, at 800 °C, the KOH-coal fly ash reaction was probably kinetically controlled. At 900-1300 °C it was diffusion limited, while at 1450 °C, it was equilibrium limited to some extent. At 500 ppmv KOH (molar ratio of K/(Al+Si) = 0.481), and a gas residence time of 1.2 s, 0.063 g K/(g additive) and 0.087 g K/(g additive) was captured by coal fly ash (D 50 = 10.20 μm) at 900 and 1450 °C, respectively. Experiments with coal fly ash of different particle sizes showed that a higher K-capture level were obtained using finer particle sizes, indicating some internal diffusion control of the process.

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Section: Methodssupporting

confidence: 75%

KOH capture by coal fly ash

Wang

Jensen

et al. 2019

Fuel

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“…Consequently, the dehydroxylation data of 800 • C and 1300 • C were not involved in the kinetic analysis. There were 34 mechanism functions used for the primary linear fitting of the dehydroxylation data of 900-1200 • C according to Equation (8) [4,24,25]. The highest linear correlation coefficient was from the random nucleation and subsequent growth model of f (α 4 ).…”

Section: Kaolinite Dehydroxylation Kineticsmentioning

confidence: 99%

“…During combustion, gasification and other processes, these semi-volatile metals are prone to cause the problems such as boiler slagging, ash deposition of heat transfer area, high-temperature corrosion, and emissions of heavy metals and ultra-fine particles [1][2][3][4][5]. Kaolinite can adsorb alkali/heavy metal vapor at high temperatures, and then be captured by dust removal equipment [6][7][8]. Therefore, the problems mentioned above can be solved by kaolinite addition into the furnace.…”

Section: Introductionmentioning

confidence: 99%

Dehydroxylation and Structural Distortion of Kaolinite as a High-Temperature Sorbent in the Furnace

Cheng

Xing

et al. 2019

Minerals

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As a high-temperature sorbent, kaolinite undergoes the flash calcination process in the furnace resulting in the dehydroxylation and structural distortion, which are closely related to its heavy metal/alkali metal adsorption characteristics. We investigated the flash calcination of kaolinite by the experiments using a drop tube furnace and by the characterization of flash-calcined products using thermogravimetric-differential scanning calorimeter (TG-DSC), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR)and nuclear magnetic resonance (NMR). There were three kinds of hydroxyl groups in kaolinite during flash calcination at 800–1300 °C, E-type (~50%, easy), D-type (~40%, difficult) and U-type (~10%, unable) according to the removal difficulty. The hydroxyl groups activation was believed to be the first step of the removal of E-type and D-type hydroxyl groups. The kinetics model of dehydroxylation groups at 900–1200 °C was established following Arrhenius equation with the activation energy of 140 kJ/mol and the pre-exponential factor of 1.32 × 106 s−1. At 800 °C, the removal of E-type hydroxyl groups resulted in the conversion of a part of VI-coordinated Al in kaolinite to V-coordinated Al and the production of meta-kaolinite. When the temperature rose up to 1200 °C, mullite was produced and a part of V-coordinated Al converted to IV-coordinated Al and VI-coordinated Al. Finally, the adsorption characteristics of kaolinite was discussed according to the results of dehydroxylation and structural distortion.

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“…A large number of studies have indicated that the main source of element K in heating surface deposits is gas phase K in biomass combustion [4,5,[8][9][10]. In this study, with the condition of combustion temperature (800 °C) and low Cl content in fuel, K probably enters the gas phase mainly in the form of KOH in place of KCl and K2SO4.…”

Section: Migration and Deposition Of Alkali Metalmentioning

confidence: 77%

“…The dominant elements in biomass ash are Ca, K, Cl and S [2,3]. During combustion, K element in biomass fuel is released to the gas phase in the form of KCl, KOH and K 2 SO 4 [4][5][6][7][8][9][10]. These potassium-containing compounds cause severe slagging due to their low melting temperature [11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Investigation of Ash Deposition Dynamic Process in an Industrial Biomass CFB Boiler Burning High-Alkali and Low-Chlorine Fuel

Zhang

Luo

et al. 2020

Energies

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The circulating fluidized bed (CFB) boiler is a mainstream technology of biomass combustion generation in China. The high flue gas flow rate and relatively low combustion temperature of CFB make the deposition process different from that of a grate furnace. The dynamic deposition process of biomass ash needs further research, especially in industrial CFB boilers. In this study, a temperature-controlled ash deposit probe was used to sample the deposits in a 12 MW CFB boiler. Through the analysis of multiple deposit samples with different deposition times, the changes in micromorphology and chemical composition of the deposits in each deposition stage can be observed more distinctively. The initial deposits mainly consist of particles smaller than 2 μm, caused by thermophoretic deposition. The second stage is the condensation of alkali metal. Different from the condensation of KCl reported by most previous literatures, KOH is found in deposits in place of KCl. Then, it reacts with SO2, O2 and H2O to form K2SO4. In the third stage, the higher outer layer temperature of deposits reduces the condensation rate of KOH significantly. Meanwhile, the rougher surface of deposits allowed more calcium salts in fly ash to deposit through inertial impact. Thus, the elemental composition of deposits surface shows an overall trend of K decreasing and Ca increasing.

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Potassium Capture by Kaolin, Part 2: K₂CO₃, KCl, and K₂SO₄

Cited by 41 publications

References 57 publications

KOH capture by coal fly ash

KOH capture by coal fly ash

Dehydroxylation and Structural Distortion of Kaolinite as a High-Temperature Sorbent in the Furnace

Investigation of Ash Deposition Dynamic Process in an Industrial Biomass CFB Boiler Burning High-Alkali and Low-Chlorine Fuel

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